Lawyers for former IMF chief Dominique Strauss-Kahn have denied fresh rape allegations, saying he has never committed violence against women.

Magistrates in Lille, in northern France, are already investigating Strauss-Kahn over his suspected role in a prostitution ring.

Now a witness statement has emerged alleging gang rape.

A Belgian prostitute has alleged the former IMF boss and three of his associates gang-raped her in Washington in 2010.

A second Belgian prostitute has partially confirmed this witness statement. Neither of the women have sought to press charges.

His lawyers, Henri Leclerc, Frederique Baulieu and Richard Malka, have issued a statement denying the new allegations.

"[Strauss-Kahn] absolutely contests having committed the slightest act of violence of any nature whatsoever," it said.

"The declarations made by these young women are contradictory.

"Distorted information, manipulation and a desire for a lynching cannot forever be a substitute for reality."

The statement also said the news of the testimony, which dates from late March, was released at an "opportune time" ahead of Sunday's run-off in the French presidential election.

Strauss-Kahn had once been the frontrunner to lead the Socialist Party against incumbent Nicolas Sarkozy in the vote.

The Socialists instead chose Francois Hollande, who is tipped to win on Sunday.

'Carlton affair'

Last May, Strauss-Kahn was arrested in New York after a hotel maid alleged he had subjected her to a sexual assault in his hotel suite.

The criminal case collapsed amid doubts about the alleged victim's testimony, but she is still pursuing a civil suit against him, and on his return to France Strauss-Kahn found himself implicated in other scandals.

The so-called "Carlton affair" centres around allegations that business leaders and police officials in the northern city of Lille operated a vice ring supplying girls for sex parties, including at Lille's Carlton Hotel.

The same ring is alleged to have supplied women for orgies attended by Strauss-Kahn in Paris, Washington and European cities and investigators believe they can prove the former finance minister committed crimes.

Strauss-Kahn has admitted to attending sex parties but denies knowing the women there were prostitutes.

Paying for sex is not illegal in France, but profiting from an organised vice ring is, and Strauss-Kahn could face a lengthy jail term.